The system and method of the invention relate to the measurement of parameters of a DC motor, and more particularly, to parameters of a field of a DC motor.
DC motors are commonly used in a variety of applications in a variety of operating environments. A DC motor may be described as having two components. These two components include a stationary part, which may be characterized as a stator, and a moving part that rotates, which is typically characterized as an armature. The armature is disposed inside the stator. There are typically four terminals, or connections to the motor. Two of the connections are to the motor""s armature through a method which allows transfer of electrical energy to the rotating part of the motor. The other two connections are to the motor""s field coils, which reside in the stator, or stationary part of the motor.
As a voltage is applied to the armature terminal of the dc motor, and another voltage is applied to the field terminals of the motor, currents flow in the armature and field coils to produce a magnetic field that serves to attract or repel the armature.
As a result, the armature spins within the stator. The armature is connected to and supported by a shaft of the motor. Accordingly, the spinning of the armature results in the spinning of the shaft. The shaft extends outside of the motor and connects to the equipment to be rotated. These components including the stator and armature of a DC motor have various operating characteristics, such as armature inductance and resistance, and field inductance and resistance characteristics. Some characteristics of a DC motor may be given by the manufacturer of the motor. However, other characteristics may need to be measured during commissioning of the DC motor, i.e., during the initial set up of the DC motor, in the particular environment in which the DC motor will operate.
DC motors are typically controlled by a control system. In order that the control system accurately control a DC motor, the various characteristics of the DC motor should be determined. For example, parameters relating to the nature of the motor""s armature need to be determined to allow for proper control of the motor. In addition, another set of parameters relating to the nature of the motor""s field must be determined for proper control of field current during normal motor operation. Among these field parameters are field resistance as well as inductance parameters. In addition, for some motor applications, it is necessary to further know the characteristics of the motor field to the extent that the magnetic field produced at various field currents is known. This relationship between field current and resulting magnetic field (flux) can be plotted with current on one axis and flux on the-other axis. It is typically called a flux curve.
There are various known methods for determining the parameters of a DC motor field However, these methods typically require that the shaft of the motor be allowed to rotate during the testing to determine the characteristics of the DC motor field . In this situation, it is often necessary to disconnect equipment in order that the shaft be free to rotate. This disconnection of equipment is also time consuming, and at times, not feasible, as should be appreciated. Accordingly, these and other shortcomings exist with known processes for measuring the operating parameters of a DC motor.
In accordance with one embodiment of the invention, a method determines the parameters of the field of a DC motor. The method comprises obtaining parameters of the DC motor; and performing an iterative processing loop, the iterative processing loop being performed n times. The iterative processing loop includes regulating field current based on the parameters of the DC motor, and calculating a field resistance from a field voltage and the field current measured during the regulating of the field current; operating in a closed loop mode to determine a first field firing angle and a second field firing angle; operating in an open loop mode to determine a first time constant and a second time constant based on applying the first field firing angle and the second field firing angle; and determining at least one parameter of the field of the DC motor based on the first time constant, the second time constant, and the calculated field resistance.
In accordance with a further aspect of the invention, the invention provides a system for determining at least one parameter of a field of a DC motor, the system comprising: a processing portion that obtains parameters of the DC motor, the processing portion performing an iterative processing loop, the iterative processing loop being performed n times, the iterative processing loop including: regulating field current based on the parameters of the DC motor, and calculating a field resistance from a field voltage and the field current measured during the regulating of the field current; operating in a closed loop mode to determine a first field firing angle and a second field firing angle; operating in an open loop mode to determine a first time constant and a second time constant based on applying the first field firing angle and the second field firing angle; and determining at least one parameter of the field of the DC motor based on the first time constant, the second time constant, and the calculated field resistance.
In accordance with a further aspect of the invention, the invention provides a system for determining at least one parameter of a field of a DC motor, the system comprising: means for obtaining parameters of the DC motor; and means for performing an iterative processing loop, the iterative processing loop being performed n times, the iterative processing loop including: regulating field current based on the parameters of the DC motor, and calculating a field resistance from a field voltage and the field current measured during the regulating of the field current; operating in a closed loop mode to determine a first field firing angle and a second field firing angle; operating in an open loop mode to determine a first time constant and a second time constant based on applying the first field firing angle and the second field firing angle; and determining at least one parameter of the field of the DC motor based on the first time constant, the second time constant, and the calculated field resistance.
In accordance with a further aspect of the invention, the invention provides a method for determining at least one parameter of a field of a DC motor, the method comprising: obtaining parameters of the DC motor; and performing an iterative processing loop, the iterative processing loop being performed n times. The iterative processing loop includes regulating field current based on the parameters of the DC motor, and calculating a field resistance from a field voltage and the field current measured during the regulating of the field current; operating in a closed loop mode to determine a first field firing angle and a second field firing angle, the operating in a closed loop mode including: regulating the current to a first high point current and measuring a first field firing angle required to obtain the first high point current; and regulating the current to a first low point current and measuring a second field firing angle required to obtain the first low point current; operating in an open loop mode to determine a first time constant and a second time constant based on applying the first field firing angle and the second field firing angle, the operating in an open loop mode including: setting an open loop firing command to the second field firing angle; stepping the open loop firing command to the first field firing angle and measuring the first time constant based on field current rate of change; and stepping the open loop firing command back to the second field firing angle and measuring the second time constant based on field current rate of change. The method further includes determining at least one parameter of the field of the DC motor based on the first time constant, the second time constant, and the calculated field resistance.
In accordance with a further aspect of the invention, the invention provides a system for determining at least one parameter of a field of a DC motor, the system comprising a processing portion that obtains parameters of the DC motor, the processing portion performing an iterative processing loop, the iterative processing loop being performed n times, the iterative processing loop including: regulating field current based on the parameters of the DC motor, and calculating a field resistance from a field voltage and the field current measured during the regulating of the field current; operating in a closed loop mode to determine a first field firing angle and a second field firing angle, the operating in a closed loop mode including: regulating the current to a first high point current and measuring a first field firing angle required to obtain the first high point current; and regulating the current to a first low point current and measuring a second field firing angle required to obtain the first low point current; operating in an open loop mode to determine a first time constant and a second time constant based on applying the first field firing angle and the second field firing angle, the operating in an open loop mode including: setting an open loop firing command to the second field firing angle; stepping the open loop firing command to the first field firing angle and measuring the first time constant based on field current rate of change; and stepping the open loop firing command back to the second field firing angle and measuring the second time constant based on field current rate of change; and determining at least one parameter of the field of the DC motor based on the first time constant, the second time constant, and the calculated field resistance.
In accordance with a further aspect of the invention, the invention provides a system for determining at least one parameter of a field of a DC motor, the system comprising: means for obtaining parameters of the DC motor; and means for performing an iterative processing loop, the iterative processing loop being performed n times, the iterative processing loop including: regulating field current based on the parameters of the DC motor, and calculating a field resistance from a field voltage and the field current measured during the regulating of the field current; operating in a closed loop mode to determine a first field firing angle and a second field firing angle, the operating in a closed loop mode including: regulating the current to a first high point current and measuring a first field firing angle required to obtain the first high point current; and regulating the current to a first low point current and measuring a second field firing angle required to obtain the first low point current; operating in an open loop mode to determine a first time constant and a second time constant based on applying the first field firing angle and the second field firing angle, the operating in an open loop mode including: setting an open loop firing command to the second field firing angle; stepping the open loop firing command to the first field firing angle and measuring the first time constant based on field current rate of change; and stepping the open loop firing command back to the second field firing angle and measuring the second time constant based on field current rate of change; and determining at least one parameter of the field of the DC motor based on the first time constant, the second time constant, and the calculated field resistance.